A water-absorbing resin (SAP/Super Absorbent Polymer) is a water-swelling and water-insoluble polymer gelling agent and has been used for mainly disposable uses including absorbing articles such as paper diapers and sanitary napkins, as well as water retention agents for agriculture and horticulture, water-stopping materials for industrial use, and the like. A large number of monomers and hydrophilic polymers have been proposed as raw materials for such a water-absorbing resin and particularly, poly(acrylic acid (salt))-type water-absorbing resins using acrylic acid and/or a salt thereof as a monomer have been industrially used most frequently owing to their high water absorbent capability.
Such a water-absorbing resin can be obtained by finely crushing a water-containing gel-like polymer, which is obtained by polymerizing an aqueous monomer solution, during or after the polymerization, and drying the obtained particulated water-containing gel-like crosslinked polymer. After drying, if necessary, a pulverizing step and a classification step are carried out and arbitrarily, the obtained product is subjected to surface-crosslinking before drying or after drying. One or more steps such as a fine powder recovery step, an undried matter removal step after drying, a packaging step, and an addition step of adding other additives (fine particles, a deodorant, an antibacterial agent, and the like) may also be carried out arbitrarily. A method to be employed as a common polymerization method is aqueous solution polymerization or reverse-phase suspension polymerization and the product form is generally a powder of about 10 to 1000 μm. Such a process for producing a water-absorbing resin involving many steps is exemplified in Patent Documents 1 to 13 or the like.